This model shows part of the ETSI (European Telecommunications Standards Institute) EN 300 429 standard for cable system transmission of digital television signals [1]. The standard prescribes the transmitter design and sets minimum performance requirements for the receiver.

The purpose of this example is to:

Model the main portions of a possible transmitter design (operating in 64-QAM mode with MPEG-2 Transport Packet data)

Model the main portions of a possible receiver design (operating in 64-QAM mode with MPEG-2 Transport Packet data)

Generate error statistics that will help determine whether the model satisfies the system performance requirements

Illustrate the use of key Communications System Toolbox™ library blocks for DVB-C (or similar) system design

There are two different versions of this example.

Floating-point version: commdvbc.slx

Fixed-point version: commdvbc_fixpt.slx

When the example model is first loaded, it creates the MATLAB workspace variable `prmDVBC`

, which is a structure with members that are used as parameters in the blocks in the model file. Note also that this workspace variable is cleared when the model is closed.

prmDVBC = bitsPerByte: 8 bitsPerMTpl: 6 MPEG2DatRateBitPerS: 9600000 rawMPEG2DataPcktLen: 184 MPEG2TrnsprtPcktLen: 188 MPEG2TrnsprtFramePer: 1.5667e-04 MPEG2PcktsPerSprFrm: 8 MPEG2TrnsSuperFrame: 1504 PRBSSeqPeriodBytes: 1503 PRBSSeqPeriodBits: 12024 RSCodewordLength: 204 CableChanFrameLen: 272 CableChanFrmPeriod: 1.5667e-04 RCosineSampsPerSym: 8 CableSymbolPeriod: 7.1998e-08 RCosineFilterSpan: 16 TxRxSymbolSampDelay: 288 DeintrlvrAlignDelay: 192 QAMSymbolMapping: [1x64 double] ConvIntlNumBranches: 12 ConvIntlCellDepth: 17

This portion of the model corresponds to sections 4.1, 5, and 6 in [1]. The MPEG-2 Transport Packet is defined in ISO®/IEC 13818-1 [2], and is comprised of 188-byte packets.

Communications System Toolbox, DSP System Toolbox™, and Simulink® library blocks are used to simulate a MPEG-2 Transport Packet data stream for system simulation and BER performance measurement purposes.

Sync1 Inversion and Randomization

This subsystem corresponds to sections 4.2 and 7.1 in [1]. The MPEG-2 `Sync1`

byte is inverted, and the data stream (other than the Sync bytes) is randomized for spectrum shaping purposes. A resettable `PN Sequence Generator`

library block is used as part of the scrambler for this data randomization process.

Shortened (204,188) Reed-Solomon Encoder

This library block corresponds to sections 4.3 and 7.2 in [1]. As described in the standard, this process adds 16 parity bytes to the MPEG-2 Transport Packet to give a (204,188) codeword. This allows up to eight (8) erroneous bytes per transport packet to be corrected by the corresponding receiver `Reed-Solomon Decoder`

block.

Convolutional Interleaver

This library block corresponds to sections 4.4 and 7.3 in [1]. The interleaving process is based on the Forney approach [3] and is compatible with the Ramsey type III approach [4], with I = 12.

Byte (8-bit) to M-Tuple (6-bit) Conversion

A `MATLAB® Function`

block is used to perform this processing. 8-bit data bytes are converted into 64-ary (6-bit) values. This block corresponds to sections 4.5 and 8 in [1].

Differential Encoding

An example implementation of the Differential Encoding unit as described in sections 4.6 and 8 in [1] is shown using a `MATLAB Function`

block. For the purposes of this example model, the Differential Encoding unit output is connected to a terminator (i.e., the unit is bypassed).

64-QAM Constellation Mapping

The `Rectangular QAM Modulator Baseband`

library block maps the baseband 64-ary (M-tuple) values to complex (I and Q) 64-QAM constellation symbol values for transmission, as described in sections 4.7 and 9 in [1].

This library block performs the baseband shaping of the complex (I and Q) constellation symbol values for transmission, as described in sections 4.7, 9, and Annex A in [1].

The System FEC as specified by the standard is designed to improve the Bit Error Rate (BER) from 10^-4 to the range, 10^-10 to 10^-11 ("Quasi Error Free" operation). The `AWGN Channel`

library block `Signal to Noise Ratio (Eb/No)`

is set to 16.5 dB corresponding to an operating BER of approximately 10^-4.

This library block performs the matched decimation filtering of the received complex (I and Q) constellation symbol values, as described in sections 4.7, 9, and Annex A in [1].

64-QAM Constellation Demapping

The `Rectangular QAM Demodulator Baseband`

library block demaps the received baseband complex (I and Q) 64-QAM constellation symbol values to 64-ary M-tuples, as described in sections 4.7 and 9 in [1].

Differential Decoding

For the purposes of this example model, the Differential Decoding portion is omitted. Additionally, a more realistic receiver system implementation will likely have equalization and synchronization processing prior to this portion of the receiver model.

M-Tuple (6-bit) to Byte (8-bit) Conversion

A `MATLAB Function`

block is used to perform this processing, which is the inverse of the Byte to M-Tuple processing used in the transmitter. 64-ary (6-bit) M-tuple values are repacked into 8-bit data bytes.

Convolutional Deinterleaver

The `Convolutional Deinterleaver`

library block corresponds to the `Convolutional Interleaver`

library block appearing in the transmitter subsystem implementation. The deinterleaving process is based on the Forney approach [3] and is compatible with the Ramsey type III approach [4], with I = 12.

For the sake of example model simplicity, a simple extra delay is used to synchronize the first sync byte into the "0" branch of the Convolutional Deinterleaver. A more realistic receiver system implementation will likely have additional upstream synchronization processing prior to this portion of the model.

Shortened (204,188) Reed-Solomon Decoder

This library block performs the R-S decoding corresponding to the encoded data packets.

Sync1 Inversion and Energy Dispersal Removal

This subsystem performs data descrambling to obtain the received MPEG-2 Transport Packet data bytes.

To examine the performance of the example, use the included visualization blocks, as listed below.

Overall System Results and Displays:

`Bit rate (Mbit/s)`

display`Cable symbol rate (MBaud)`

display`64-QAM bit error rate (BER)`

display`System bit error rate (BER)`

displayVarious internal bit error rate (BER) displays (under the

`Internal Tx and Rx BER`

subsystem)

Transmitter/Receiver Results and Displays:

`Tx 64-QAM Constellation`

scatter plot`Rx 64-QAM Constellation`

scatter plot`Tx/Rx Spectrum (2MHz BW)`

scope`Total Number of Errors Corrected`

display

There are two different versions of this example -- a floating-point version and a fixed-point version. The examples are similar. In particular, most of the `Transmitter Baseband Processing`

and `Receiver Baseband Processing`

subsystems are identical, and mainly use unsigned integer data types in their signal paths.

The differences between the two versions are in how the signals are processed by the `Byte to M-tuple Conversion`

, `64-QAM Constellation Mapping`

, `Square Root Raised Cosine Tx Interpolation Filter`

, `Square Root Raised Cosine Rx Decimation Filter`

, `64-QAM Constellation Demapping`

, and `M-Tuple to Byte Conversion`

blocks. These blocks use floating-point (and built-in integer) arithmetic when their input and/or output signals are floating-point (i.e., data type `double`

or `single`

) or purely built-in integer (e.g., `uint8`

), as is the case in the floating-point version (commdvbc.slx).

In the fixed-point version (commdvbc_fixpt.slx) however, these blocks use fixed-point arithmetic because their input and/or output signals are fixed-point data types (i.e., `sfix`

or `ufix`

in Simulink). Also note that a Fixed-Point Designer™ license is required to run the fixed-point version of the example.

The following simulation results show matching BER performance for the chosen settings when comparing the floating-point version with the fixed-point version.

[1] *ETSI Standard EN 300 429 V1.2.1: Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for cable systems*, European Telecommunications Standards Institute, Valbonne, France, 1998.

[2] *ISO/IEC 13818-1*, "Coding of moving pictures and associated audio."

[3] Forney, G., D., Jr. "Burst-Correcting Codes for the Classic Bursty Channel." *IEEE Transactions on Communications*, vol. COM-19, October 1971, pp. 772-781.

[4] Ramsey, J. L. "Realization of Optimum Interleavers." *IEEE Transactions on Information Theory*, IT-16 (3), May 1970, pp. 338-345.

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